The present invention relates generally to an improved swirler and fuel injector for a gas turbine engine combustor, and, more specifically, to an improved swirler and fuel injector for independently supporting primary and secondary recirculation zones within the combuster to extend operating range.
Systems for mixing air and fuel so as to establish stable recirculation zones where combustion can occur in a gas turbine are well-known in the art and take various forms. Gas turbine combustors used in aircraft engines also need to operate over a range of fuel-to-air ratios, as the total flow of fuel is varied to adjust the power output of the engine. A rich fuel-air ratio is desired at low fuel flow for stable combustion while a lean fuel-air ratio is desired at high fuel flow to reduce smoke. A typical swirler-fuel inejctor assembly employs a central fuel injector disposed within an assembly of air swirlers receiving pressurized air from the gas turbine compressor at the inlet end of a gas turbine combustor. Atomized fuel is sprayed into the air flow from a pressure atomizing spray nozzle or fed in from an airblast atomizer, so that atomization of the fuel will be largely accomplished by high velocity air flow.
In modern high temperature gas turbine combustors, especially those utilized in aircraft engines, the maximum possible fuel-air ratio operating range is desired between flame blowouts, i.e. extinguishing of flame, on engine deceleration transients, and the high power limit, imposed by visible smoke production. Techniques previously used to extend the operating range include variable geometry combustors, double annular combustors, and selective fueling, i.e., supply of fuel only to selected fuel nozzles at low power.
Variable geometry combustors have the disadvantage of added cost, weight and decreased reliability of the complex mechanical arrangement required to vary the combustor geometry.
Double annular combustors employ two coannular rows of swirlers with independently varied fuel flow from injector nozzles in the inner and outer rows. This arrangement also has disadvantages due to the relative complexity thereof.
In selective fueling, the swirlers are arranged in a single row, whereby fueled, and selectively fueled-unfueled nozzles alternate. Such designs frequently encounter undesirable carbon accumulation in the nozzles which are shut off during portions of the engine's operating time when burning liquid hydrocarbon fuels.
Accordingly, it is an object of the present invention to provide a new and improved swirler fuel injector for a gas turbine engine combustor which will extend the operating range of a gas turbine at varying fuel-air ratios.
Another object of the invention is to provide an improved swirler and fuel injector for separately fueling primary and secondary recirculation zones in a gas turbine combustor from a central fuel injector.
Another object of the invention is to provide an improved swirler and fuel injector with a geometry which will extend the operating range and is adaptable to the existing geometry of an aircraft gas turbine engine.
Another object of the present invention is to provide an improved co-annular swirler and fuel injector suitable for bimodal fuel injection in a gas turbine combustor.